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This invention relates to a fuel injection system, and more particularly to a fuel control apparatus for an internal combustion engine.
A fuel injection system for an internal combustion, aircraft engine generally includes, among other components, a fuel injection servo, a flow divider, and fuel nozzles. Conventional fuel injection servos are shown in FIGS. 1-4. FIGS. 1 and 2 show the RSA-5AD1 and the RSA-5AB1 fuel injection servos, respectively, sold by Precision Airmotive Corporation. FIG. 3 shows the RSA-7AA1 fuel injection servo, which is also sold by Precision Airmotive Corporation.
The major components of a conventional fuel injection servo include the airflow section, the flow metering section, and the fuel regulator section. The RSA-5AB1 servo also includes an automatic mixture control section. Each of these sections cooperates in a known manner to regulate the amount of fuel that is delivered to the engine, which is proportional to the amount of air that flows through the throttle body assembly, i.e., the power produced by the engine. A portion of the internal components of a conventional fuel regulator assembly is shown in FIG. 4, which shows a stack of components that cooperate to separate air and fuel chambers about an air and fuel diaphragm, respectively. The air and fuel diaphragms are also interconnected by the associated components, and each imparts a force on the regulator stem that is connected to the ball, which regulates the position of the ball valve to thereby regulate the metering head across the jetting system (not shown) and thus the amount of fuel delivered to the engine.
A description of the fuel injection systems utilizing the RSA-5AD1 and RSA-5AB1 servos are provided in RSA-5 and RSA-10 Fuel Injection Systems, Operation and Service Manual, by The Bendix Corporation and Training Manual, RSA Fuel Injection Systemxe2x80x9d by Precision Airmotive Corporation, the entirety of each being incorporated into the present application by reference. A description of the fuel injection systems utilizing the RSA-7AA1 servo is provided in RSA-7AA1 Fuel Injection System, Operation and Service Manual, by Precision Airmotive Corporation and Airflow Performance High Performance Fuel Metering Systems, Installation and Service Manual, by Airflow Performance, Inc., the entirety of each being incorporated into the present application by reference.
To insure that a fuel injection system operates properly after assembly, the fuel injection servo must be calibrated. In a conventional fuel control system, the fuel servo must be calibrated as a single unit. That is, for example, in the RSA-5AD1 servo of the prior art, the fuel metering and regulator sections must be attached to the airflow section, and the entire servo must then be calibrated as a single unit. Calibration of the unit entails, for example, the application of a pressure signal to the fuel regulator and properly shimming the servo seat, the center body seal, and adjustment of the regulator stem, fastening bolts, and other components. Likewise, the components of the fuel metering section need to be calibrated, which involves pressure testing. Because the calibration of the conventional fuel injection servo must be performed as a single unit, the unit becomes a single, fixed system that cannot be easily modified.
This cumbersome calibration method is somewhat alleviated in the RSA-7AA1 servo. With this servo, the fuel metering and fuel regulator sections are calibrated together as a unit, separate from the air flow section. After calibration of the fuel metering and fuel regulator sections together, they can be installed onto the air flow section without the need to perform further calibration of the servo unit. However, in the RSA-7AA1 servo, once the fuel metering and fuel regulator sections are calibrated together as a unit, it becomes a fixed unit. Any change in either the fuel metering or regulator sections requires recalibration of the two sections as a unit, even if only one section is changed.
This conventional design approach to fuel injection servos does not lend itself to quick turn around time if changes to the fuel metering section or fuel regulator section are required, either for operational purposes or for maintenance. For example, with a conventional fuel injection servo, such as the RSA-5AD1 and RSA-5AB1, in order to make a modification in either the fuel metering section or the fuel regulator section, the entire fuel injection servo would have to be recalibrated as a single unit. Such an operation is extremely time consuming and expensive. Likewise, with the RSA-7AA1 servo, changes in either the fuel metering section or the fuel regulator section require recalibration of the fuel metering/fuel regulator unit. Additionally, in a fuel injection servo where the airflow section and fuel metering section are an integral casting, such as in the RSA-5AD1 and RSA-5AB1 servos, a modification in the fuel metering section requires replacement of the airflow section as well.
Therefore, there is a need to provide a fuel injection servo that does not require calibration as a single unit when modifications and/or replacement of the fuel metering section or fuel regulator section is required.
Accordingly, one implementation of the present invention provides a fuel control apparatus (i.e, a fuel injection servo) with a fuel metering section and fuel regulator section that can each be calibrated independently of each other, and independent from the airflow section. The fuel control apparatus of the present invention includes a modular air passage mechanism (i.e., a modular airflow section) and a modular fuel pressure modifying mechanism (i.e., a modular fuel metering section). The modular air passage mechanism has an air intake end and an air outlet end, and is constructed and arranged to accommodate airflow therethrough. The modular fuel pressure modifying mechanism is constructed and arranged to receive fuel from a fuel supply and deliver the fuel at a pressure that is different from the fuel supply to a modular fuel regulator mechanism (i.e., a modular fuel regulator section). The modular fuel regulator mechanism is constructed and arranged to communicate with the airflow in the air passage mechanism and the modular fuel pressure modifying mechanism to regulate an amount of fuel delivered to the engine. Each of the modular fuel pressure modifying mechanism and the modular fuel regulator mechanism are removably mountable to the modular air passage mechanism independently from each other.